Various types of drainage systems are used to transport waste fluid from a source to a desired collection point. Gravity drainage systems, for example, use the pull of gravity to transport waste fluid. Such systems have many drawbacks. For example, options for the layout of gravity drainage piping are limited since the piping must be located below the waste fluid source and must continuously slope toward the collection point. The waste fluid source is often located on a concrete pad, so piping must be laid out before the concrete is poured. In addition, it is overly difficult to renovate or add plumbing to a gravity drainage system due to the piping location requirements, and personnel are often displaced during renovation, resulting in loss of production time.
Vacuum drainage systems provide an alternative to conventional gravity drainage piping. Such systems typically comprise a vacuum source connected to a collection tank. A main drainage pipe is attached to the collection tank, and one or more collection branches fluidly communicate with the main drainage pipe. Each collection branch typically includes a vertical riser section having an interface valve disposed therein. A buffer for collecting waste fluid from a source is attached to a bottom end of the riser.
In operation, waste fluid initially collects in the buffer. When a fluid level is sensed in the buffer, the interface valve is opened to transfer vacuum to the buffer. The vacuum acts on a downstream side of the buffer, while an upstream side is open to atmosphere. As a result, the vacuum creates a pressure differential across the fluid in the buffer which pushes the fluid up the riser to the main drainage pipe in the form of a discrete volume or slug of waste fluid. During normal operation, the interface valve remains open for an additional period of time to pull a volume of air into the system behind the slug to ensure that the fluid is transported to the main drainage pipe. Depending on the capacity of the vacuum source, the vacuum created in the riser is capable of transporting fluid up vertical lifts, thereby allowing for greater flexibility in locating piping. As a result, vacuum drainage systems simplify installation and renovation of plumbing fixtures.
In many applications, the plumbing fixture always supplies a low volume flow of waste fluid to the buffer, so that the vacuum drainage system operates as described above. Certain plumbing fixtures, however, are capable of delivering a high flow of waste fluid which may cause the system to stall. For example, a vacuum drainage system used to collect waste fluid from a refrigerated case normally receives a low volume flow of condensate from the case. The case, however, is periodically washed, creating a high flow situation. If a wash down occurs when the system has a low vacuum level, a portion of each slug will not reach the top of the riser and will flow back into the buffer. Over time, the riser will become filled with a solid column of fluid. The vacuum source attached to the main vacuum pipe is often sized for a particular riser lift and slug size and, therefore, is often not capable of lifting the solid fluid column through the riser. As a result, the system stalls, unable to accept additional waste fluid, and waste fluid may back up through the buffer and flood the surrounding area. The only previously known solution for preventing such stalling is to select a vacuum source having a greater capacity, which is overly costly and unnecessary during normal operation. Moreover, lifting the solid fluid column up certain lifts is beyond capabilities of any type of vacuum source, and therefore the stalling problem is unresolved.